In minimally invasive medical interventions, in which a medical instrument, such as a catheter, stent or biopsy needle, is inserted into the body of a patient and therefore can generally no longer be captured visually by eye directly, it is necessary, for example to navigate the medical instrument in the body of the patient, to overlay an image of at least the relevant part of the instrument on image information from inside the patient's body. A physician carrying out the navigation operation, e.g. an interventional radiologist, a neuroradiologist or a cardiologist, wants to be informed at all times during the navigation operation about the position of the instrument in relation to the respective anatomy of the patient, in order to be able to navigate in the safest and most precise manner possible.
Until now navigation of instruments inserted into a patient's body has frequently taken place using x-ray images, for example using x-ray fluoroscopy images, in which the respective instrument can be seen. Progress in the miniaturization of instruments and the use of new materials for instruments means that said instruments can no longer be identified or can only be identified with difficulty in x-ray images. Changing the x-ray intensity for imaging such medical instruments in x-ray images represents a health risk, specifically during longer medical interventions, in particular for clinic personnel, carrying out interventions on a continuous basis.
One alternative to navigating an instrument using x-ray fluoroscopy images is to use an optical or electromagnetic tracking or location system. When using an optical tracking system for example one or more optical markers or reflectors are arranged specifically at the proximal end of the instrument, which protrudes out of the body, it being possible to capture these using a camera system of the optical tracking system. The specific arrangement of the markers on the medical instrument makes it possible to determine the position of for example the tip of the instrument in the patient's body in relation to a coordinate system assigned to the optical tracking system. The use of an optical tracking system is however generally hereby restricted to rigid medical instruments.
When using an electromagnetic tracking system the use of a number of transmitters allows a number of electromagnetic fields to be generated for example, in which the medical instrument provided with corresponding sensors is moved inside the patient's body. The electrical signals induced in the sensors can also be used in this manner, with a specific arrangement of the sensors on the medical instrument, to determine for example the tip of the medical instrument in a coordinate system assigned to the electromagnetic tracking system.
Both when using an optical tracking system, like the “Polaris” system from Northern Digital Inc., Waterloo, Ontario, Canada, and when using an electromagnetic tracking system, like the “Aurora” system from Northern Digital Inc., Waterloo, Ontario, Canada, for medical applications of the navigation system it is necessary to register the respective coordinate system of the tracking system with an image coordinate system of an x-ray system or another imaging system, in order to be able to overlay an image of at least a part of the medical instrument on image information relating to the patient obtained with the x-ray system or another imaging system, based on the positions of the medical instrument obtained using the tracking system.
U.S. Pat. No. 6,649,914 B1 discloses an imaging system with x-ray scanning, with which the positions of a catheter inserted into a patient's body and provided with an x-ray sensor can be determined in a plane. The imaging system comprises a scanning x-ray beam source, whose x-ray target is only stimulated point by point by an electron beam to emit so-called pencil beams, with the x-ray target being scanned in a specific form with the aid of a scan generator using the electron beam. If x-ray radiation is detected with the x-ray sensor of a catheter, it is possible to determine the x and y positions of the respective catheter in a plane using the scan data from the scan generator.